The present invention relates to a control system for correcting torque variation in an internal combustion engine.
Conventionally, as a process for improving a catalyst purification rate, an air-fuel ratio (A/F) is intermittently switched between lean and rich during a warming-up stage at a cold-start time of an internal combustion engine to cause fire at the catalyst in order to raise the temperature of the catalyst. Such switching-over between lean and rich may cause torque variation that is synchronized with a switching cycle.
Besides, regardless of the presence or absence of such switching-over of the air-fuel ratio, there occurs a vibration having a certain cycle in the engine rotational speed due to a torque variation of each cylinder caused by deterioration over time or the like.
Since these variations are not desirable from a drivability viewpoint, there are some known techniques for offsetting the torque variation by changing a retard amount for an ignition timing in accordance with a value of the air-fuel ratio (refer to the Japanese Patent No. 2867747).
However, the magnitude of torque variation may vary in accordance with operational conditions and/or individual properties of the internal combustion engines. Besides, there exists such torque variation that is not dependent on the switching-over of the air-fuel ratio. Accordingly, in some cases, it is not possible to control the torque variation according to the conventional approaches.
Thus, there is a need for a technique for precisely detecting the state of an excessive torque variation.